Field of the Invention
The present invention relates to a kinematic support structure, and in particular to that of a “groove-groove-groove” type.
Description of the Related Art
A kinematic support structure is a support structure for repeating a relative positional relationship between two bases with high precision and avoiding deformation by releasing the differences in thermal expansion between the bases. A conventional kinematic support structure comprises a base (first base) wherein three ball-like protrusions (balls) are fixed and another base (second base) facing this.
FIGS. 7 and 8 schematically show an example of a construction for a conventional kinematic support structure. FIG. 8 (a) (b) and (c) represent cross-sectional views taken along line VIIIa-VIIIa, line VIIIb-VIIIb and line VIIIc-VIIIc in FIG. 7 respectively. Ball-like protrusions 30, 40 and 50 are provided and fixed on a first base 10. The ball-like protrusions 30, 40 and 50 abut on a second base 20, thereby determining the relative positional relationship between the first base 10 and the second base 20 uniquely.
The ball-like protrusions 30, 40 and 50 abut on V-shaped grooves 21, 22 and 23 of the second base 20 respectively in two points. Thus, the first base 10 and the second base 20 contact in six points, thereby restricting six degrees of freedom (X, Y, Z, θx, θy, θz) representing the relative position and determining their positions.
FIG. 9 schematically shows another example of a construction for a conventional kinematic support structure. The example adopts a “plane-groove-cone” construction instead of the “groove-groove-groove” construction shown in FIG. 8. The ball-like protrusion 30 abuts on a plane portion 24 in a single point, the ball-like protrusion 40 abuts on a V-shaped groove 22 in two points and the ball-like protrusion 50 abuts on a conical concave portion 25 with a circle (or in three points). Thus, the first base 10 and the second base 20 contact in the three points and a circle (or in the six points) in total, thereby restricting six degrees of freedom (X, Y, Z, θx, θy, θz) representing the relative position and determining their positions.
As an example of a construction for such a kinematic support structure, a construction described as conventional art in Japanese Patent Application Laid Open No. 2008-159632 can be referred to. FIG. 9 of the document discloses an example of the “plane-groove-cone” type and an example of the “groove-groove-groove” type.
Also, Japanese Patent No. 4836940 (corresponding to U.S. Pat. No. 8,413,948) describes an example of a construction wherein a portion of the kinematic support structure is modified. FIGS. 1A-1D of the document disclose an example of the “plane-groove-cone” type.
Regarding the “plane-groove-cone” type, the use of spheres which are not fixed to any base instead of the ball-like protrusions is known. FIG. 6 of Japanese Patent Application Laid Open No. 2006-78187 discloses an example of such a construction.
In order for the “groove-groove-groove” type of kinematic support structure to function ideally, it is necessary that the first base and the second base contact via the ball-like protrusions and that points of contact between the ball-like protrusions of the first base and the second base move (slide) without any resistance. However, conventional techniques have a problem in that there may be friction between the ball-like protrusions of the first base and the second base. Examples of detrimental phenomena caused due to the friction are: positional precision of the bases degrades; the structure is displaced or deformed because detrimental force is exerted; etc.
Note that, regarding the “plane-groove-cone” type as described inJapanese Patent Application Laid Open No. 2006-78187, it is known to use spheres which are not fixed to any base. However, even those skilled in the art would not conceive of combining such a construction with the “groove-groove-groove” type. For example, in FIG. 6 of Japanese Patent Application Laid Open No. 2006-78187, none of the balls are fixed to the bases, so if this construction is applied to the “groove-groove-groove” type without any modification, it would appear that it would not function as a positioning and locating structure.